The present invention relates to a color picture tube having an internal magnetic shield or, more particularly, to a construction for mounting the internal magnetic shield on a mask frame.
A prior art color picture tube having an internal magnetic shield disclosed in JP-Y2-59-27010 (UM) is known. This construction will be described with reference to FIG. 3. A glass bulb 1 forming a housing includes a panel 1b with a phosphor screen 1a formed on the interior surface thereof, a funnel 1c fusion-bonded to this panel 1b by a low-melting-point crystal glass (not shown) and having an interior conductive film (not shown) on the interior surface thereof, and a neck 1d coupled to the funnel 1c.
The panel 1b has arranged therein a shadow mask 3 which selects an electron beam from an electron gun 2 disposed on the neck 1d and causes the electron beam to impinge on the phosphor screen 1a. A peripheral skirt of this shadow mask 3 is secured to a mask frame 4. An end of a spring plate 5 is fusion-bonded to several points along the periphery of the mask frame 4, and the other end of the spring plate 5 is formed with a hole which is adapted for engaging a support pin (not shown) provided on the interior surface of the peripheral part of the panel 1 so that the mask frame 4 is supported by the panel 1b. Also, an internal magnetic shield 6 extending toward the neck 1d is fixed by a fixing spring 7 on a flange 41 of the mask frame 4. This belt-like fixing spring 7 is bent into the shape shown. The ends 71, 72 of this spring 7, as illustrated in FIG. 4, are held against the spring pressure and inserted into rectangular holes formed in the flange 41 of the mask frame 4 and the flange 61 of the internal magnetic shield 6, after which the fixing spring is released, thereby securing the internal magnetic shield 6 on the mask frame 4 by spring action. The internal magnetic shield 6 is secured to the frame 4 by the fixing spring 7 before the funnel 1c is fusion-bonded to the panel 1b.
In the aforementioned prior art apparatus, the internal magnetic shield 6 is only kept in pressure contact with the mask frame 4 by the fixing spring 7, and therefore, an external force such as a vibration that may be exerted on the glass bulb 1 would cause the mask frame 4 and the internal magnetic shield 6 to slide with each other at the coupling thereof. As a result, the blackened film (Fe.sub.3 O.sub.4) formed on the surface of the mask frame or the internal magnetic shield would be damaged and separated, or burrs that may have been created during the processing of the flanges 41, 61 might be separated. Small pieces of burrs and blackened film thus separated, if attached to the shadow mask 3, would clog the mask aperture, or if attached to an electrode, would induce a spark.